Hundreds of couples toting AR-15 rifles packed a Unification church in Pennsylvania on Wednesday (local time) to have their marriages blessed and their weapons celebrated as "rods of iron" that could have saved lives in a recent Florida school shooting.

Women dressed in white and men in dark suits gripped the guns, which they had been urged to bring unloaded to the church in the rural Pocono Mountains, about 160 kilometres north of Philadelphia.

Many celebrants wore crowns — some made of bullets — while church officials dressed in flowing bright pink and white garments to go with their armaments.

Reverend Moon said in a statement that the staff of the Florida school should have been armed, an option President Donald Trump has said should be explored nationwide and which teacher unions have criticised.

"Each of us is called to use the power of the 'rod of iron' not to arm or oppress as has been done in satanic kingdoms of this world, but to protect God's children," he said, citing the Book of Revelation in the Bible.

"If the football coach who rushed into the building to defend students from the shooter with his own body had been allowed to carry a firearm, many lives, including his own, could have been saved."

The Pennsylvania school district three years ago called off classes during the massive manhunt for survivalist Eric Frein, who police said used an AK-47-style weapon to ambush a Pennsylvania state trooper barracks and then fled into the mountains.

Frein was found guilty last April of killing a Pennsylvania state trooper and wounding another in the September 2014 attack.

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